The present invention relates to providing color proof images of inks on a printing stock prior to a production or press run.
In order to approximate the appearance of continuous-tone (photographic) images via ink-on-paper printing; the commercial printing industry relies on a process known as halftone printing. In halftone printing, color density gradations are produced by printing patterns of dots of various sizes, but of the same color density, instead of varying the color density uniformly as is done in photographic printing. There is an important commercial need to obtain a color proof image before a printing press run is made. It is desired that the color proof will accurately represent the image quality, details, and color tone scale and, in many cases, the halftone pattern of the prints obtained on the printing press. In the sequence of operations necessary to produce an ink-printed, full-color picture, a proof is also required to check the accuracy of the color separation data from which the final three or more printing plates or cylinders are made. Traditionally, such color separation proofs have involved silver halide photographic, high-contrast lithographic systems or non-silver halide light-sensitive systems which require many exposure and processing steps before a final, fall-color picture is assembled. U.S. Pat. No. 4,600,669 to Ng et al., for example, discloses an electrophotographic color proofing system.
In color proofing in the printing industry, it is important to be able to match the proofing ink references provided by the International Prepress Proofing Association. These ink references are density patches made with standard 4-color process inks and are known as SWOP (Specifications Web Offset Publications) Color References. For additional information on color measurement of inks for web offset proofing, see xe2x80x9cAdvances in Printing Science and Technologyxe2x80x9d, Proceedings of the 19th International Conference of Printing Research Institutes, Eisenstadt, Austria, Jun. 1987, J. T. Ling and R. Warner, p. 55. Preferred dyes and dye combinations found to best match the SWOP Color References are the subject matter of commonly assigned U.S. Pat. No. 5,024,990 to Chapman and Evans, 5,023,229 to Evans and Chapman, and 5,134,116 to Chapman and Evans, the disclosures of which are incorporated by reference.
In the past, images for the printing industry were prepared on black and white films, with each color record on a different film. A proof of the complete image could be prepared from these films by a variety of photosensitive systems, by contacting the film with the colored photosensitive material, exposing the assembly to bright light, and then developing the photosensitive material to remove the non-imaged areas, and finally assembling the four colored images into the complete image. During the past few years, the printing industry has shown a willingness to embrace digital images which can be imaged, pixel by pixel, directly onto printing plates, without the intervention of film. In this case, accurate digital color proofs are essential to predict the results of the press run without the expense of making a proof on the press.
There remains a commercial need for an accurate, low cost method for preparing a color proof of a digital image in the graphic arts industry.
It is therefore an object of the present invention to prepare low cost accurate color proofs of digital images using ink jet printing with a special receiver that can be laminated to the final printing press stock paper.
This object is achieved by a method of forming color proof images of inks on a printing stock prior to a production or press run, comprising the steps of:
a) providing a receiver having a peelable substrate, such receiver including a layer having a mordant in a binder formed over the substrate which will form a bond with colorant in the ink and an ink-receiving layer formed over the mordant layer which is permeable to ink, but which restricts spreading of ink as it passes through such layer to the mordant layer;
b) depositing ink having colorants onto the ink-receiving layer to form a color proof image in the mordant layer; and
c) laminating the ink-receiving layer to the printing stock and removing the peelable substrate from the receiver to form a color proof.
This object is also achieved by providing a receiver having a peelable substrate with a layer having a mordant in a binder over the substrate which will mordant the ink image, and an ink-receiving layer over the mordant layer which is permeable to ink, but which restricts spreading of ink as it passes through the ink-receiving layer to the mordant layer. The image is deposited onto the ink-receiving layer to form a color proof in the mordant layer and laminated to a printing stock paper after which the peelable substrate is removed to form a color proof.
Color proofs made in accordance with the present invention can use ink jet printing techniques, which are economically advantageous.
The proofs are made on the same paper as the press run, providing an accurate rendition of the color hues and densities.
The present invention permits a press operator to adjust the press conditions to provide printed impressions of the colored hues and densities desired by the customer.